Adobe After Effects CC Classroom in a Book (2019 Release), First Edition

Select the Window Lit layer, and press T to reveal its Opacity property.

Click the pick whip icon ( ) on the Opacity property line for the Window Lit layer, and
drag it to the Opacity property name in the Background Lit layer. When you release the
mouse, the pick whip snaps, and the first Opacity property is red.

Expand the Opacity property for the Window Lit layer. An expression in the Window Lit
layer time ruler now reads “thisComp.layer(′′Background Lit′′). transform.opacity.” This
means that the Opacity value for the Background Lit layer (0%) replaces the previous
Opacity value (100%) for the Window Lit layer.

Drag the current-time indicator from 0:00 to 5:00. Notice that the Opacity values for the two
layers match.

Go to the beginning of the time ruler, and then press the spacebar to preview the animation